The Theory of Tectonic Plates

The Theory of Plate Tectonics

The Earth’s lithosphere (crust and upper mantle) is divided into tectonic plates.

These plates move on top of the asthenosphere (lower mantle).

We know that these plates move in different ways.

Tectonic Plates

Tectonic Plate Boundaries

A boundary is a place where tectonic plates touch.

There are 3 types of tectonic plate boundaries:

Convergent Divergent Transform

The numbers on the map represent the rate at which plates are moving in centimeters.

Plate Movement

Convergent Boundary

• When two plates collide, or move toward each other, the boundary is called convergent

• There are 3 types of convergent boundaries, depending on what type of crust comes together.

• Continental-continental• Continental-oceanic• Oceanic-oceanic

What forms at a Convergent Boundary?

MOUNTAIN RANGES

Dense oceanic crust sinks below the continental crust and sinks into the asthenosphere.

This is a subduction zone. A VOLCANO

What forms at a Convergent Boundary?

What forms at a Convergent Boundary?

►One oceanic plate sinks below the other.

►Another subduction zone►A VOLCANO

What forms at a Divergent Boundary

Two tectonic plates move away from each other. On the sea floor at the mid-ocean ridge this is called

sea floor spreading. As the plates move apart, magma rises to fill the gaps. The magma is cooled and forms new ocean floor.

The volcanic country of Iceland, which straddles the Mid-Atlantic Ridge, offers scientists a natural laboratory for studying on land the processes also occurring along the submerged parts of a spreading ridge. Iceland is splitting along the spreading center between the North American and Eurasian Plates, as North America moves westward relative to Eurasia.

Mid Ocean Ridge- Atlantic Ocean

Divergent Boundary

On-land exposure of the Mid-Atlantic Ridge in Iceland.

Sea Floor Spreading

What forms at a Transform Boundary?

Two tectonic plates move past one another.

Their edges are jagged and irregular.

As they grind together and jerk, they slide past each other creating earthquakes.

Possible Causes of Plate Movement• Convection Currents: hot rock deep in

the Earth rises, cooler rock sinks. This movement of magma causes plates to move

• Ridge push• Slab pull

Tracking Tectonic Plate Movement• Plates move very slowly, centimeters to inches a

year.• GPS, Global Positioning System, measures the

rate of movement.• Radio signals beam continuously from satellites

to the Earth.• By recording the time it takes for the Ground

station to move a given distance, scientists can measure the speed at which plates move.

• Plate Boundary Animation• http://www.classzone.com/books/earth_science/t

erc/content/visualizations/es0804/es0804page01.cfm?chapter_no=visualization

• http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm